According to Patent specification SE 8502327-3 (452 279) a robot with a positioning head, the robot comprising at least three setting devices which can be extended and shortened in longitudinal direction, is already known. Each setting device is secured in a fixed frame via a first joint so that each setting device is pivotable in all directions in relation to the frame. Each setting device is also attached at one end in a movable positioning head via a second joint. A rigid arm is also joined to and emanates from the positioning head between the setting devices, the arm being radially guided but axially displaceably journalled in a universal joint relative to and rigidly connected to the frame.
A similar robot is also known in which the setting devices are secured in a displaceable runner via a first joint, the runner being secured in a fixed frame, so that each setting device is pivotable in all directions in relation to the frame. The joint is thus indirectly secured in the frame.
These known robots are controlled by each setting device being provided with a motor to extend or shorten the setting device. Control is effected by the setting devices being controlled linearly to a predetermined location of the positioning head or the positioning head being controlled along a predetermined pattern of movement. There is thus no control of the set location of the positioning head, which means that the influence of force and temperature on the setting devices, joints, positioning head, etc. results in a difference between the desired set point and the actual position.
This difference between set point and actual position is unsatisfactory and leads to reduced accuracy in the use of the robot.